Diesel engines are well known for being highly durable and fuel efficient. Because of the durability and fuel efficiency, diesel engines have long been used in heavy-duty motor vehicles, such as trucks, buses and locomotives.
Historically, diesel engines have been operated on a petroleum-derived liquid hydrocarbon fuel boiling in the range of about 300° F. to about 750° F. (149° C.-399° C.). Generally, a diesel fuel is a mixture of normal paraffins, branched paraffins, cycloparaffins (i.e., naphthenes), olefins, and aromatics. The aromatic content in a typical diesel fuel is in the range of about 20% to 45% by weight. Studies have shown that diesel fuels with a high aromatic content are prone to emit pollutants upon combustion. The pollutants include, for example, solid particulate matter (e.g., soot) as well as gaseous pollutants (e.g., unburned hydrocarbons, carbon monoxide, and nitrogen oxides). Minimizing the production of pollutants from vehicles operating with diesel fuels is important for both environmental and health reasons. Ever increasingly stringent specifications are being adopted in order to reduce pollutant emissions from diesel fuels. In California, for example, starting in October, 1993, the California Air Resources Board (CARB) mandated a maximum aromatics content for commercial diesel fuels of 10 volume percent (9.5 wt. %).
In addition to a relatively high aromatic content, a majority of diesel fuels also have a sulfur content on the order of several hundred parts per million or more. The presence of sulfur in diesel fuels constitutes a serious environmental hazard. Hence, strict regulations limiting the amount of sulfur which may be present in such fuels have been introduced. Unfortunately, most currently available fuels with a suitably low sulfur content exhibit poor inherent lubricity, and this can lead to problems when the fuel is used. For example, the use of low sulfur fuel in diesel engines frequently results in damage to the fuel injector pump which relies on the natural lubricating properties of the fuel to prevent component failure.
For the foregoing reasons, there is a need for a diesel fuel composition which has a lower aromatic content and a lower sulfur content. It would be desirable that this diesel fuel composition possess the requisite properties for use in a diesel engine.